Objective lens of extremely high relative aperture



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INVENTOR ALBRECHT W. TRONNIER BY W Mfi w JW ATTORNEYS United StatesPatent 1 2,861,500 OBJECTIVE LENS OF EXTREMELY HIGH RELATIVE APERTUREAlbrecht Wilhelm Tronnier, New York, N. Y., assignor to Farrand OpticalCo., Inc., New York, N. Y., a corporation of New York ApplicationNovember 14, 1955, Serial No. 546,381 6 Claims. (Cl. 88--57) Thisinvention relates to a very fast objective for photographic purposes,particularly for the photography of fast-moving objects underunfavorable light conditions, for example in motion picture andtelevision work.

For such uses objectives are required having a relative aperture greaterthan f/ 1.5 and a total field angle of about 25, and in which forachievement of high definition the primary and zonal sphericalaberration must over the entire aperture be kept below some 1 of theequivalent focal length and in which moreover the astigmatic errors mustbe kept below i of the equivalent focal length over the entire field.

Objectives having these properties have hitherto been available only forrelative apertures up to about f/ 1.8. Insofar as the relative aperturesof such systems have been extended substantially beyond f/ 1.8, forexample to f/1.3 or f/1. 2, it has almost automatically followed thatthe primary and zonal spherical errors were substantially increased orthat the astigmau'c errors increased to some 1% of the focal length ormore, or else the useful field was reduced to 10 or at most In most ofthe previous proposals indeed two or more of these deleterious effectsappeared as concomitants of such increase in relative aperture.

These disadvantages of the very rapid objectives hitherto available areovercome by the present invention, which makes possible an increase inrelative aperture to f/ 1.2 or beyond while retaining the high degree ofcorrection in spherical and astigmatic errors above mentioned over theentire system aperture and over the entire field. Ac-

cordingly the new objectives of the invention represent a substantiallyimproved means made available to photographic practice, particularly inthe taking of photo- I. A doublet having the shape of a positivemeniscus concave toward the diaphragm which follows, the doublet beingcomposed of a biconvex positive element L and of a biconcave negativeelement L on the diaphragm side of the positive element.

II. A meniscus element L;, of positive power, also concave toward thediaphragm, the convex front surface of this meniscus presented to thelong conjugate side being more strongly curved than the correspondingfront surface of the doublet I which precedes it.

III. A meniscus element L, of positive power having for its two surfacesthe same signs respectively as have the corresponding surfaces ofcomponents I and II.

The convex front surface of this element, which is presented to thecomponents I and II, is more strongly curved than is the correspondingsurface of compo- 'ice 2 r DIA. A diaphragm disposed in the large airspace between components IV and V.

V. As the last component of the objective, a conver-.

gent element L, of high power having surfaces of unequal curvature,positioned on the short conjugate side of the diaphragm.

The new objective according to the invention can be schematicallydescribed as follows, with reference to the.

identification of its components I, II, HI, IV, DIA and V:

I II III IV DIA V diaphragm +U Here the plus and minus signs identifythe sign of the powers. The letter D identifies component I as adoublet. The letter M characterizes the components II and III ascomponents of meniscus shape, and the letterU characterizes componentsIV and V even more broadly as components having unequally curvedsurfaces.

The distribution of power among the components preceding the diaphragmon the long conjugate side is indicated by the following scheme:

I 11 III IV Here the plus and minus signs for the first component referof course respectively to the first and second ele- In theseinequalities R is the front radius of the positive component II, R isthat of the component IH, R, is the radius of the rear surface of thenegative component IV, and R is the front radius of the last componentV, all with respect to the front radius R of the doublet I. It will beremembered that this doublet is composed of 1 two elements L and L, ofopposite power to form tovergent surface presented to the succeedingdiaphragm being likewise concave.

gether the convergent meniscus-shaped front component whose exteriorsurfaces like those of the following positive meniscus components H andIII are concave toward the diaphragm.

It is known that for the achievement of a relatively simple make-up ofan optical system the distribution of power among the various componentsis important. This is particularly true for systems of high relativeaperture, as in the case of the present invention. This criterion leadsto the following definition of characteristic properties of the lensesof the invention:

(1) The sum of the surface powers of the two exterior surfaces of thedoublet I, which are concave toward the diaphragm, is greater than 16%but less than 40% of the equivalent power of the entire objective.

(2) This surface power sum of the exterior surfaces of the doublet I isbetween 24% and 48% of the sum of the surface powers of the two surfacesof the positive Patented Nov. 25, 1958 meniscus III, which among thecomponents on the long conjugate side of the diaphragm is the lastpositive one and has the greatest positive power.

(3) The sum of the surface powers of the two surfaces of the convergentmeniscus II is between 60% and 140% of the sum of the surface powers ofthe two exterior surfaces of the doublet I.

In this connection it will be remembered that the surface power of anair-glass interface having a radius of R or R millimeters (according asit is a front or rear surface) is measured in diopters as a function ofthe glass index n according to either of the following wellknownformulas:

For passage from air to glass: =lO (n l)/R, For passage from glass toair: ',-=1000(l-n,-)/R'.;

Here, for the powers of the separate surfaces, the subscript i will beallowed to assume successively the values 1-5, correspondingrespectively to the components I-V. The surface power sums of thecomponents may then be written as follows:

A further feature of the invention lies in the choice of power for thepositive component V on the image side of the system. Thus consistentlywith the foregoing, the

sum of the surface powers of the two air-glass inter faces of thiscomponent is between 400% and 760% of the sum of the surface powers ofthe front doublet I. This fourth property may be written as follows:

The surprising significance in the performance of the lens of thisadditional dimensional criterion may be explained by considering that ifthe power of the component V were decreased below the minimum value 4.0thus specified the result must be an excessive concentration of positivepower in the components I-IV in order to retain sufiicient over-allpower and speed for the objective. There would then result a substantialincrease in the errors of high aperture bundles and in the interimediate zonal aberrations thereof. If on the other hand the power of thecomponent V were increased beyond the maximum value of 7.6 the resultwould be an excessive concentration of power on the image side of thesystem. This would result not only in a marked increase in distortionbut also in a noticeable and undesirable field curvature.

It further appears that in addition to the advantages already mentionedit is possible to achieve for the objectives of the present invention avery great reduction in the difierence between the sagittal andmeridional image surfaces by so proportioning the powers of thedivergent concave rear faces of the positive meniscus components II andIII that the sum of the surface powers of those faces is between -2.25and 5.75 times the sum 5 of the surface powers of the front doublet I.In this way there is provided with respect to the doublet such an excessof astigmatic overcorrection in components II and III that theundercorrection introduced by the doublet is not only fully compensatedbut further there remains such an excess of overcorrection as to makepossible in conjunction with the operation of the components IV and Vachievement of the previously specified image performance over theentire field. Thus, algebraically:

The lenses illustrated in Figs. 1 and 2 bothembody the characteristicproperties of the invention which have just been discussed. Two specificexamples of lenses according to the invention will now be described. Thetable entitled Example 1, Table 1 gives data for a lens of the typeillustrated in Fig. l,and that entitled Example 2 gives data for a lensof the type illustrated in Fig. 2. In these tables R and R, withnumbered subscripts corresponding to the successive components, arerespectively the radii of the exterior front and rear airglassinterfaces of the components. At the chromatically overcorrecting pairof adjacent surfaces enclosed within the doublet, R is the radius of thefront surface of the biconcave rear element, and R' is the radius of therear face of the biconvex front element of this doublet. The axialspacing, if any, of these surfaces of radii R and R' is identified as a.The axial thicknesses of the lens components are identified by theletter i with appropriate subscripts and the axial spacings of thecomponents are similarly identified by the letter s. 'The glasses areidentified by Abbe numbers 11 and refractive indices n,

referred to the yellow helium line d of 5876 Angstrom units wave length.

Example 1, Table 1 (linear dimensions in mm.) [Equivalent focal lengthf=l00.00 mm. Relative aperture f./1.2.]

Thickness Component Lens n v Rudll t, Spacing s or Gap a B1 =+l08.38 Ll1.62056 60. 0 ti =l9.200

R =200.l2 I a=0.l15

R =l99.89 L2 1. 6199:) 36. 4 t1=6.600

81 =0.G66 R2 =+72.02 II L: 1.62056 60.0 t: =16.658

R! =+10a3s 82 =0.573 Ra =+47.96 III L4 1.65833 51.0 t; =16.658

IV L 1.75524 27. 6 t4 =I1.140

R; =+30.74 Diaphragm s =16.658

R5 =+56.70 V L 1.74414 45.0 is =8.901 R's =199.89

In the lens of Example 1 the radii of the surfaces presented to the longconjugate side of the system are related as follows:

The distribution of surface powers and power sums Example 1 thusexhibits, within the range of power distribution according to theinvention, the following specific power relations:

The surface power sum is 11.800 diopters and hence )=4.05 4:

The lens of Example 1 can be regarded as typifying the construction ofobjectives according to the invention. Taking the equivalent focallength as unity and neglecting the small air space within the frontdoublet, it can be represented in round numbers as set forth in theaccompanying Example 1, Table 2:

Example 1, Table 2 Lens 11. v Radii Thickness t or Spacing 8 R =+1.1fL 1. 62 60 it =02! RN=2f RNR N cemented toget er R =2f L: 1.62 36 t'0.1f

81 0.1f R =+0.7f L3 1.62 60 ta=0.2f

R; =+l.1f

8: 0.1 1' Rs =+0.5f L 1. 66 51 t3 =0.2f

R's =+1.1f

as 0.1I R4 f L5 1. 76 27 t4 =0.1f

S4 =0.2f R =-|0.6f L6 1. 74 45 t5 =0.1f

, R's =2f The objective of Example 2, which is illustrated in Fig. 2,was designed as an objective lens for amateur motion picture camerashaving an equivalent focal length of inch, corresponding to 23.4 mm.Here the front radius R of the doublet I is 1.000 inch so that therelations among the various radii may be readily inferred. Its data aregiven herewith:

Example 2 (linear dimensions in inches) [Equivalent focal length [=59/64in. Relative aperture 171.2,]

By comparison with that of Example 1, a simplification is achieved inthe objective of Example 2 by an altered choice of glasses. I is madeequiconvex, and in this way in'Example 2, two curvatures are eachemployed three times-in spite of the large aperture of f/ 1.2 achievedand without sacr i fice of the highly corrected properties specified atthe outset of the description of applicants invention. The two radii inquestion are 1.0000 and 2.0336 inches.

Example 2 strikingly shows how the components of the objective of theinvention may be defined by use of the front radius R, of the doublet Ias a unit of reference. With this point of departure the relations amongthe five components of Example 2 may be set forth as follows:

Example 2 further shows the achievement of an additional simplificationin that the adjacent surfaces R' and R are provided with equal radii andare cemented together. This pair of surfaces is strongly overcorrectingfor chromatic errors, since a v-difference of 24.0 applies thereto.Consequently the front doublet I carries a substantial portion of thecolor correction of the objective. As a result of its constructionaccording to the invention from a binconvex element together with abiconcave element, it permits such a distribution of radii and power asis specified by the invention, which makes possible not only theoreticaldesign but particularly easy manufacture of the lens.-

While the invention has been described herein in terms of a number ofpreferred embodiments, various changes may be made therein withoutdeparting from the scope of the invention, which is set forth in theappended claims.

I claim:

1. A high speed optical objective system comprising. from front to back,a doublet of meniscus shape and positive over-all power including apositive biconvex front element and a biconcave negative rear element,first and second positive meniscus components having convex frontsurfaces, a negative component having surfaces of unequal curvature,and, behind the diaphragm position, a positive rear component havingsurfaces of. unequal curvature, the sum of the surface powers of theouter surfaces of the doublet lying between 0.16 and 0.40 times thetotal power of the system and between 0.24 and 0.48 times the sum of thesurface powers of the second positive meniscus component, the sum of thesurface powers of the first positive meniscus component lying between0.60 and 1.40 times the said sum of the surface powers of the doublet,the radii R R and R of the convex I front surfaces of the two positivemeniscus and rear components respectively and the radius R' of theconcave rear surface of the negative component having surfaces ofunequal curvature being related to the radius R of the convex frontsurface of the doublet as follows:

2. A high speed optical objective system according to claim 1 in whichthe sum of the surface powers of the rear component lies between 4.0 and7.6 times the sum The biconcave element of the doublet of the surfacepowers of the exterior surfaces of the doublet.

3. A high speed optical system according -to claim 2 in which the sum ofthe powers of the rear surfaces of the two positive meniscus components'lie between -,2.25 and 5.75 times the sum of the surface powers of theouter surfaces of the doublet.

4. A high speed optical objective system comprising, from front to back,a positive doublet. component includmg a positive front element L and anegative rear element L first and second positive memscus components Land L :1 negative component L and, behlnd the diaphragm position, apositive rear component L said system conforming substantially to thefollowing conditions:

Element In- Abb Radil Thickness t or dex No. Spacing s Rt =+1.1f L1 1.62 60 t1 =O.2f

RN= f RNRN cemented together RN =2 f L: 1.62 36 t'1 0.1f

81 0.1f Ra =+0.7f L; 1.62 60 l2=0.2f

8s 0.1 f R; =+0.5f L 1.66 51 t==o.2j

R's =+1.1f

ra 0.1f R4 f Ls 1.76 27 t4=0.1f

R'r =+0.3 f

a4=0.2f R5 =+0.6f L 1. 74 45 ts=0.1f

R's =2 f v in which 1 is the equivalent focal length of the system.

5. A high speed optical objective system comprising, from front to back,a positive doublet component including a positive front element L and anegative rear element L first and second positive meniscus components Land L a negative component L and, behind the diaphragm position, apositive rear component L said system conforming substantially to thefollowing conditions:

said system having a focallength of substantially mm. and a relativeaperture of substantially f/ 1.2.

6. A high speed optical objective system comprising, from front to back,a positive doublet component includ ing a positive front element L and anegative rear element L first and second positive meniscus components Land L a negative component L and, behind the diaphragm. position, apositive rear component L said system conforming substantially to thefollowing conditions:

said system having a focal length of substantially inch and a relativeaperture of substantially f/ 1.2.

References Cited in the file of this patent UNITED STATES PATENTS1,812,717 Rudolph June 30, 1931 1,839,011 Bieliche .l Dec. 29, 19312,346,061 Altman Apr. 4, 1944 2,366,597 Cox Jan. 2, 1945 2,387,497 CoxOct. 23, 1945 2,413,476 Warmisham et a1. Dec. 31, 1946 2,433,438 CoxDec. 20, 1947

